The invention relates to an electromechanically and hydraulically operable motor vehicle brake having an actuator assembly, comprising: a housing, an actuator element that is displaceable relative to the housing for hydraulic or electromechanical displacement of a brake lining, a motor drive, a displacement mechanism arranged between the motor drive and the displaceable actuator, gear arrangement assigned to the displacement mechanism and a separate self-locking device which is designed to lock the displacement mechanism as needed, wherein the displacement mechanism has a ball screw drive having a spindle and a nut, wherein the one component can optionally be driven rotationally by a spindle nut drive, and the other component can be displaced linearly inside the housing as a spindle nut for displacement of the actuator element by rotational drives of a component of the spindle nut.
For a long time, motor vehicle brakes have been in use, in which the brake linings are hydraulically displaced in the usual manner in the case of normal operational braking while driving the vehicle, but in which for activation of a parking brake function, an electromechanical displacement of the brake linings or at least an electromechanically triggered locking of the brake linings in a braking position takes place. Such motor vehicle brakes offer the advantage that the parking brake function can be activated or released more conveniently by simple operation of an activation switch.
Such electromechanically and hydraulically operable motor vehicle brakes are known from the state of the art.
The document WO 2008/037738 A1 thus describes a motor vehicle brake that can be operated both hydraulically and electromechanically. In a normal operational situation, i.e., while driving the vehicle, this motor vehicle brake is hydraulically operated in the usual way. However, for activation of a parking brake, the electromechanical operating function is activated. In doing so, an electric motor is triggered, driving a spindle nut arrangement via a displacement mechanism with a gear arrangement. The gear arrangement is designed to be self-locking with a worm gear to prevent the parking brake effect from being diminished when the parking brake is activated. However, the self-locking effect has the disadvantage that only very low degrees of efficiency can be achieved, so that the components, in particular the electric motor, must be designed to be relatively powerful and must have a high power consumption. It is true that the total efficiency of the system is comprised of the product of the individual efficiencies of the components. For example, efficiency is derived from the product of the efficiency of the motor, the efficiency of the downstream gear arrangement and the spindle nut arrangement. Thus, efficiencies in the range of only 30% and less can be achieved with gear arrangements having a self-locking effect.
The document DE 10 2012 208 294 A1 describes a motor vehicle brake in which a separate self-locking device is arranged directly on the nut-spindle assembly. Reference is made particular to FIG. 8 in this document, where it is shown that the self-locking device, which is designated as coupling device 41, is arranged between the rolling body ramp gear and the brake piston. Such a direct spatial correlation of the self-locking device with the spindle nut assembly and a ball screw drive has the disadvantage that the reactive forces occurring in activation of the brake and maintenance of a (parking) brake state must be absorbed by the self-locking device to the full extent. The self-locking device must be designed to be solid accordingly, as a result of which it takes up a substantial amount of space. Therefore, the brake must also be designed to be disproportionately large in the axial direction in particular with respect to the threaded spindle.
Furthermore, the document DE 10 2011 102 860 A1 discloses a motor vehicle brake that has been improved in comparison with this prior art, in which the self-locking device is arranged close to the spindle nut arrangement but is integrated into the gear arrangement, so that the installation space can be reduced in the axial direction with respect to the threaded spindle. This brake can be designed to be more compact.
The document DE 10 340 250 A1 describes an electric parking brake for a motor vehicle comprising a first electric drive. The first electric drive serves to switch the parking brake between an active position and a released position. To improve the efficiency of the parking brake with respect to the known parking brakes having a self-locking gear speed, this arrangement provides another component in the form of a second drive. This second drive can be moved between a locking position and a position that releases the parking brake. The first drive in this arrangement is free of any self-locking effect.
DE 19 750 420 A1 describes an electrically operable brake for a motor vehicle, which includes a parking device. The parking device has a ratchet wheel, which is connected to a drive for the brake in a rotationally fixed connection. Furthermore, the parking device has two pawls that can be retracted into the ratchet wheel. These pawls can be displaced by means of a motor drive to mechanically lock the ratchet wheel and thus the brake by engagement of the pawls in the ratchet wheel.
Additional prior art is known from the document DE 10 2011 084 190 A1, which discloses an electrically operable motor vehicle brake having a parking brake device. The parking brake device is equipped to keep the motor vehicle brake de-energized in a parking brake position. To do so, a permanent magnet in a rotationally fixed arrangement cooperates with a yoke, which is provided in a drive train of the brake. Permanent magnetic attractive forces thus cause a noncontact rotational locking in the drive train. However, the parking brake device can be stopped by generating a magnetic field directed against the magnetic field of the permanent magnet and thus neutralizes the effect of the permanent magnet.